The present invention relates to a tire having a radial carcass reinforcement which is intended to bear heavy loads and is inflated to relatively high pressures, and in particular to an aircraft tire.
The radial carcass reinforcements of such tires generally comprise a plurality of plies of textile reinforcement elements, which are anchored within each bead to at least one annular reinforcement element and most frequently to a single bead wire. The reinforcement elements of said reinforcements are wound around said bead wire from the inside to the outside, forming upturns the respective ends of which are spaced radially relative to the axis of rotation of the tire. The harsh conditions under which aircraft tires are used are such that the endurance of the beads is low, in particular at the level of the upturns of the carcass reinforcement.
A significant improvement in the performance is obtained by separating the plies of the carcass reinforcement into two groups. The first group comprises the axially inner plies of the carcass reinforcement in the zone of the sidewalls and beads, said plies then being wound around an anchoring bead wire within each bead, from the inside to the outside of the tire. The second group is formed of at least one axially outer ply in the zone above, which ply is generally partially wound around the bead wire, from the outside to the inside of the tire. Such arrangements are known and are disclosed for example in U.S. Pat. No. 4,244,414 (FIG. 2 of said patent).
The endurance of the beads thus constituted may be improved by the presence within each bead of an additional reinforcement ply wound around the bead wire and thus forming an axially outer strand and an axially inner strand, said reinforcement ply being the ply closest to the filling or infill rubber profiled element, which is generally triangular and radially above the anchoring bead wire. An architecture of this type is disclosed in U.S. Pat. No. 5,285,835.
Likewise a solution was proposed consisting of arranging the edge(s) of said axially outer ply (plies) between the upturns of the axially inner plies.
The endurance of the beads of aircraft tires is however in need of improvement, in particular when said beads are subjected to great overloads which may impart thereto loadings of the order of 50% of their height and more. The progress to be expected of development of the architecture of the beads would seem, at least at present, to be fairly limited, owing to the very fact of the necessary number of carcass plies, generally formed of reinforcement elements of aliphatic polyamide, in order to withstand the tension due to what is called the test pressure which, as is known, must be equal to four times the operating pressure. The large number of said carcass plies obviously involves the multiplication of the free ends of reinforcement elements, the multiplication of the interfaces between plies, greater hysteresis losses and therefore higher operating temperatures, all of which are factors favorable to increasing the fatigue of the beads and limiting their endurance.
The solution proposed by the present invention to improve the endurance of the beads of an aircraft tire lies in the replacement of the carcass plies of aliphatic polyamide by carcass plies formed of composite reinforcement elements, that is to say ones formed of yarns of different moduli.